The invention relates to a method of metering highly viscous, paste-like material, in particular printing ink, e.g. offset printing ink, from a metering valve, wherein the metering valve in dependence upon the determined quantity of material delivered into a container or the like is closed and then the residual material left suspended at the outlet side of the metering valve is removed, as well as to a metering device for metering highly viscous, paste-like material.
Metering highly viscous, paste-like material which, for example, has a viscosity in excess of 2000 pascal/sec is difficult in practice, as becomes particularly clear, for example, when attempting to meter different offset printing inks into a container in such a way that the mixed product obtained is of a precisely defined shade of colour.
It is known to supply highly viscous, paste-like materials in the form of offset printing inks from drum-shaped containers under high pressure each to a metering valve, from which a stream or strand of the material is then discharged into a container coupled to a weighing device, so that the metering process, generally controlled by a computer, is terminated when the preselected quantity of material has been discharged from the metering valve. The offset printing inks of other colour shades are correspondingly discharged via further metering valves into the container to thereby obtain the desired mixture of material of a preselected colour shade.
While good control of the metering valve may be achieved despite the high viscosity of the paste-like material being discharged, so that the desired quantity of material is metered with sufficient accuracy into the container or the like, a considerable problem is presented by the fact that, after closure of the metering valve, a certain amount of residual material is left suspended from its underside, the quantity depending on the composition of the material, the ambient temperature or the like, i.e. not being precisely defined. Apart from the fact that the discharge of said residual material into the container containing the metered material leads to an inaccuracy which may considerably alter the mixing ratio, it is also extremely difficult to remove said residual material from the underside of the valve.
In practice, removal of the residual material is frequently effected with the aid of a spatula, to which, however, the residual material then adheres and has to be scraped off by hand at a receiving container. The residual material is therefore generally left clinging to the edge of the receiving container and contaminates said container, making it no longer easy to close with a lid.
An attempt has already been made to remove the residual material by providing air nozzles in the region of the underside of the metering valve in order to use the air jets exiting from such nozzles to detach the residual material suspended from the underside of the metering valve. Apart from the fact that this would, at best, lead to the substantially unknown quantity of residual material additionally falling into the container already containing the desired quantity of material and hence invalidating the metering, in many cases owing to the irregular action of the air jets an approximately lateral spinning-away of the residual material was effected so that the residual material fell outside of the region of the container onto the floor or even soiled the clothing of the operator. Stains caused by printing ink in particular are extremely stubborn and are removable, if at all, only with great difficulty.